In iron-making processes, sintered iron ore, which is mainly manufactured from hematite ore, is charged in a blast furnace to produce metallic iron. To manufacture sintered iron ore, the hematite ore, which is a main material, is mixed with carbonaceous materials, additives (e.g. calcium oxide (CaO) or the like) and iron-containing by-products (dust, sludge, mill scale, etc.) and then heated to a temperature ranging from 1300 to 1480° C. In order to prevent the breakage of the sinter when it is transported and charged into a blast furnace, high cold strength is required. In addition, fine powder generation due to volume expansion of about 20% and consequent internal stress in the sinter when hematite is reduced to magnetite should be minimized while maintaining a high reducibility index.
Meanwhile, magnetite ore is mainly obtained in the form of ultrafine powder (about 0.2 mm or less) and has a low reducibility index, and thus the usability thereof in an iron-making process is limited. More specifically, when magnetite ore is directly used as sintered iron ore, cracking cannot be expected when hematite is reduced into magnetite. Accordingly, internal gas diffusion becomes slow, and it is difficult to realize high reducibility. Hence, most techniques that have been developed for manufacturing sintered iron ore use hematite as a main material. For this reason, upon manufacturing the sintered iron ore, the magnetite ore is used in a manner in which a portion thereof is combined with hematite ore. However, when the magnetite is used as a main material, it is anticipated that there is no problem of fine power generation during the reduction, unlike hematite. The magnetite ore is a candidate material to be utilized as sintered iron ore as long as it satisfies cold strength and high reducibility index. Since the magnetite is obtained in the form of ultrafine powder, it must be subjected to a sintering process in order to be used for the iron-making operation in a blast furnace.
Furthermore, techniques, known to date, that utilize magnetite ore include: the formation of compounds having low melting points by irradiating a mixture of magnetite (or hematite) and CaO with microwaves; and manufacturing hematite pellets from a green pellet of a magnetite-water-flux-binder mixture. However, a technology for directly utilizing sintered magnetite ore in an iron-making process has not yet been introduced.
Korean Patent Application Publication No. 10-2004-0034995 discloses sintered iron ore having a high reducibility index and low reduction degradation and a method of manufacturing the same, in which a flux additive is used in a large amount, and consequently the slag volume is increased during the blast furnace processing. Therefore, the coke ratio is undesirably increased.